1. Field of the Invention
The present invention is directed to a video standard selection circuit which selects between a default video standard and one of multiple video standards indicated by a user and, more particularly, to a system in which a state machine sets a video standard mode to a default mode and then cycles through possible video modes providing a user an opportunity to select a desired mode other than the default mode.
2. Description of the Related Art
In the design of video systems, adherence to several video signal standards may be required, particularly for video systems which will be used in more than one country. In some cases, a particular video unit, such as a compact video disk player, may only require adherence to one signal standard, another unit of the same system may require adherence to a different standard while a third unit of the same system may need to be switchable between three or more standards. As an example, consider an application specific integrated circuit (ASIC), manufactured by the same or different manufacturers, which will be used in several systems such that the ASIC must adhere to B-PAL, M-NTSC and SECAM video standards. If a particular system that uses this integrated circuit is to be used primarily in the M-NTSC environment, then it should default to the M-NTSC standard. However, another system using the same integrated circuit design may be used primarily in the B-PAL environment and thus should default to the B-PAL standard. In addition, systems using this integrated circuit may be required to switch among several different standards but default to the same standard each time they are powered up. As a result, means is needed to specify the standard to which an application specific integrated circuit defaults upon power up and means is needed to switch the operating mode of the integrated circuit between more than one standard after power up, if so desired. One method of selecting between one of two default modes and allowing overriding of the default mode by the user is to provide a default pin which may be either left open circuit or tied to ground. When the signal from the default pin is combined by an Exclusive-Or circuit with a programmable bit which can be set by a user, the user will be allowed to override whichever default setting is selected. However, such a simple circuit does not allow default to more than two standards or the selection by the user between three or more standards when overriding a particular default selected. What is needed is the ability default to several different standards and to selectably override the default.